With a DIY circuit to measure the turbidity of water, students can put water samples to the test and explore the way engineers evaluate water clarity. In a new environmental engineering project, students model a water treatment plant process to test one of the ways water is changed from murky to clear before being piped to customers for drinking—and then use their homemade turbidity meter to evaluate the results.

Photo: Steve Hillebrand, US Fish and Wildlife Service

More than 18 million people drink water sourced from the Mississippi River and its tributaries. Parts of the river, unfortunately, contain so many contaminants that the National Park Service deems the water unsafe for fishing, swimming, and drinking. You would not want to scoop up a jar of water for drinking directly from the source, but that water may still make it into home drinking water. It takes science to make river water, and water from other ground and surface sources, safe to drink.

That science happens inside a water treatment plant.

Cleaning Water

In the new From Turbid to Clear: How Flocculation Cleans Up Drinking Water science project, students take a closer look at one of the key processes water from surface sources like lakes and rivers undergoes in a water treatment plant—the use of flocculants to remove solid debris and particles. While not all impurities in water can be seen, floating particles and debris can. If you scoop river water into a jar and shake or stir it, you may see solids floating in the water. Not all contaminants that can make water unsafe to drink are visible, but no one wants to drink water that looks dirty or has things floating in it!

At a water treatment center, flocculants are used to help floating particles (total suspended solids) combine so that they are weighted down and settle to the bottomthe bottom where they can be removed. As particles are removed, water that was turbid (not clear) becomes clear. This is an important step in cleaning water for drinking.

Environmental Engineering and the Chemistry of Clean Water

In the From Turbid to Clear advanced environmental engineering project, students simulate processes scientists use to treat and test water for drinking. Students first build a homemade turbidity meter that enables them to measure the resistance between an LED and a photoresistor when a water sample is placed in between. The more turbid the water, the more resistance the turbidity meter should show. How much difference does the clarity of the water make? Students explore first by creating and testing a series of standards with their turbidity meter and then move on to a controlled experiment in which they add alum powder (a flocculant) to water samples to explore the process (and measurable results) of water cleaning.

How much alum powder is needed to turn turbid water clear? How well does a turbidity meter work to gauge the cleanness of water? These are questions students can investigate with this combination circuit-building and chemistry project.

Making Connections

Students interested in questions related to water purity, including filtering, cleaning, and desalinating, may also enjoy science projects and activities like these:

You can find this page online at: https://www.sciencebuddies.org/blog/flocculants-and-the-science-behind-clean-drinking-water

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